1. Field of the Invention
The present invention relates to a device and a method for identifying a person using the biological information of the person, or in particular the finger vein pattern of the person.
2. Description of the Related Art
Now that the security technique for personal belongings and information is considered critical, the biometrics identification using the biological information of the person is closely watched as a personal identification technique high in utility and confidentiality. The conventional biometrics identification techniques using the fingerprints, the iris, the voice, the face, the veins in the back of the hand or the finger veins have been conceived. Especially, the identification technique using the finger vein, which can be accomplished simply by applying light to the finger, has the great advantages of a low psychological resistance and a high anti-falsification characteristic due to the use of the internal information of an organism.
The identification using the finger veins is implemented in the following manner. Specifically, the infrared light incident on a finger from the back or side surface thereof is scattered in the finger and radiated outside. In the process, the hemoglobin in the blood absorbs more infrared light than the surrounding tissue. In the case where the image of the light radiated and transmitted from the thick of the finger is picked up, therefore, the blood vessels, i.e. the finger veins distributed under the skin of the thick of the finger are visible as a pattern of a dark shadow. This image is registered in advance, and the correlation is determined between this image and the image of an object finger to be checked. In this way, it is possible to determine whether the person involved is registered or not for personal identification.
An identification device using the finger veins is disclosed in JP-A-7-21373. This personal identification device has the feature that an image of a finger is picked up by attaching an optical fiber closely to the finger to minimize the loss of light power for picking up the image. JP-A-2002-83298, on the other hand, discloses a device and a method of personal identification operated in an environment requiring no-contact detection using an image of a finger vein pattern. Also, the device disclosed in JP-A-2003-30632 comprises a finger guide unit and a fingertip button switch to assure uniform image pickup conditions for each case of matching the finger vein pattern for identification.
The conventional techniques use a guide unit for fixing a finger in position or guiding the finger to the correct position in the identification device to pick up an image of the finger veins with a high reproducibility. The finger is inserted along the guide unit, so that the factors of fluctuations of the finger shape including the angle of the finger joints, the three-dimensional rotation angle of the finger about the center axis thereof and the distance from the camera are suppressed, thereby making it possible to pick up an image of the finger vein pattern with a highly reproducible shape.
The user not accustomed to the operation of the identification device, however, may erroneously insert or deform the finger by bringing the finger into contact with the finger guide unit, applying so strong a force to the finger as to bend the finger joint or inserting the finger at variable angles. The user who has long used the device, on the other hand, though capable of inserting the finger with a high reproducibility, may place the finger in a different way than at the time of registration for a reduced correlation with the registered pattern. Also, a willful user may insert a false finger of other than an organism or a finger with a falsified pattern attached thereon for registration or identification.